Explain thermal expansion and contraction with examples like electric wires, railway tracks, and thermometers.

Here are the answers to your questions:

Question 2:
The learners were investigating the thermal expansion of a metallic string. They were observing how the length of the string changes when heated.

Question 3:
Electric overhead wires are not fixed tightly on poles to allow for thermal expansion and contraction. Metals expand when heated (e.g., by the sun in summer) and contract when cooled (e.g., in winter). If the wires were taut, they would snap due to tension during contraction in cold weather or sag excessively during expansion in hot weather, damaging the poles or the wires themselves.

Question 4:
Here are four examples of how expansion and contraction of matter are applied in daily life:

• Gaps in railway tracks and expansion joints in bridges are left to allow the metal to expand in hot weather without buckling.
• Bimetallic strips are used in thermostats and fire alarms. They bend due to the different expansion rates of two metals, activating a switch.
• Riveting involves heating rivets, inserting them, and allowing them to cool. As they cool, they contract, pulling the plates together tightly.
• Liquid-in-glass thermometers work on the principle of thermal expansion. The liquid (mercury or alcohol) expands when heated and contracts when cooled, indicating temperature.